Reprocessing of spent fuel by the PUREX process leads to generation of high-level liquid waste (HLLW). Presences of the long-lived minor actinides in the waste essentially determine its long-term hazard potential. Keeping in view of the long-term strategy for the management of the waste, it is desirable that the waste be subjected to partitioning to devoid the actinides from HLLW. This technology will pave the way for subjecting the actinides either to transmutation or immobilizing them in suitable host materials for their long term management.
The presently known processes as TRUEX, DIAMEX and solvents such as TRPO, diglycolamides made it possible to extract trivalent actinides in organic solvents from HLLW. But in all these processes trivalent lanthanides resulting from the fission were also extracted along with actinides in the organic phase. The back extraction of the organic phase results in the aqueous phase containing both the trivalent actinides and lanthanides. However, in order to further improve the control of waste materials, it would be of vital interest to separate minor actinides from lanthanides. Accordingly, efficient separation processes continue to be sought, and this is the context in which most current researches on ligand design were being carried out.
Group separation of trivalent actinides from lanthanides is difficult because they tend to form similar coordination complexes with ligands due to their similar charge densities. These separations however, can be accomplished by utilizing the fact that a small degree of covalency in the bond between actinide-ligands exists over lanthanide ligands. The increased covalency results in actinide elements having slightly higher affinity for soft donor ligands having N and S donor atoms. Using this principle various extractants have been developed.
The sulphur containing extractants like dithiophosphoric acid, bis(2,4,4,trimethyl pentyl)dithiophosphinic acid and bis(dichlorophenyl)dithiophosphinic acid are described by C. Musikas, G. Le Marios, R. Fitoussi and C. Cuillerdier, Actinide separations, ACS Symposium Series, Vol. 117, 1980; R. Fitoussi, C. Musikas, U.S. Pat. No. 4,461,747; Y. Zhu, Radiochimica Acta, 68, 95-98, 1995; Y. Zhu, J. Chen and Rongzhou Jiao, Solv. Extr. Ion Exch. 14(1), 61-68, 1996; G. Modolo, R. Odoj. Solv. Extr. Ion. Exch., 17 (1), 33-53, 1999. However, their susceptibility to degradation under process conditions limits their use.
Nitrogen containing extractants like TPTZ, nPr-BTP, and TPEN are described by M. Bonnin, C. Musikas, P. Vitorge, U.S. Pat. No. 4,496,523, 1985; Z. Kolarik, U. Mullich, F. Gassener, Solv. Extr. Ion Exch., 17(5), 1155-1170, 1999: T. Matsumura and K. Takeshita, J. Nuc, Sci. Tech., 43, 7, 824-827, nPr-BTP and their derivatives are superior in selectivity and efficiency, however their performance is reduced due to degradation during practical use. TPTZ and TPEN alone have weak interaction with trivalent actinides and used in a synergistic combination with a lipophillic cation exchanger having hard donor oxygen atom for better extractability.
Thus there is a need to provide an extractant, which overcomes the problems of the compounds as taught in the prior art.
The present inventors have found that the subject compounds of the present invention differ entirely by their chemical structure where both soft donor nitrogen atoms and hard donor oxygen atoms are incorporated in the molecule to attain the separation without use of second extracting agent. The numbers and positions of donor atoms in the molecule are appropriately integrated in order to meet the requirements of favorable complex formation with trivalent actinides over lanthanides.